An ink cartridge stores ink to be supplied to an inkjet recording device (inkjet printer). The ink cartridge is provided with an ink storage chamber that stores ink and an ink supply port that supplies ink from the ink storage chamber to the inkjet printer. The ink supply port may also function as an insertion port for an ink extraction tube. When the ink cartridge is not mounted to the inkjet printer, the ink supply port is closed by a valve so that ink will not leak from the ink cartridge.
Mounting the ink cartridge to the inkjet printer is performed by pressing the ink cartridge toward the inkjet printer. In the inkjet printer, a hollow ink extraction tube is protrudingly arranged. When the ink cartridge is mounted to the inkjet printer, the ink extraction tube engages the valve that closes the ink supply port of the ink cartridge, and the ink supply port is opened. By opening the ink supply port, the ink storage chamber and the ink extraction tube are permitted to communicate with each other, and ink is supplied to the inkjet printer via the ink extraction tube.
JP-A-2005-22198 discloses an ink cartridge including an ink supply port having a valve that is urged into a closed position by a coil spring. The ink supply port is opened when the ink cartridge is mounted to an inkjet printer and an ink extraction tube opens the valve by acting against an urging force of the coil spring. When the valve is opened by the ink extraction needle, the ink supply port can supply ink through the ink extraction needle to the inkjet printer.
JP-A-2005-103866 discloses an ink cartridge including a valve element that does not employ a coil spring. The valve element is constructed so as to be slightly deformed by insertion of an ink extraction tube. The slight deformation opens an ink supply port and permits the supply of ink.
However, in the ink cartridges disclosed in JP-A-2005-22198 and JP-A-2005-103866, the respective ink flow paths have round cross sectional shapes. Thus, if air is present in the respective ink flow paths, the ink flow paths can be easily blocked by that air. Air is generally present in spherical bubbles within an ink flow path, so if the cross sectional shape of the ink flow path is round, the ink flow path can be easily closed by the bubbles. In particular, the smaller the ink flow path diameter in a valve body of an ink cartridge, the easier it is for ink flow path blockage to be caused by air. Obstructions to an ink flow path lead to problems with the supply of ink to an inkjet printer.